1. Field of the Invention
The present invention generally relates to the manufacture of three dimensional stack package devices, and more particularly, to an automated stacking and soldering apparatus and a manufacturing method for three dimensional stack package devices.
2. Background of the Related Art
As the integration of semiconductor IC devices increases and IC devices become larger, there is a need to enhance their mounting density. To meet this need, three dimensional stacking technologies have been developed and widely employed in assembly processes by semiconductor manufacturers. In a three dimensional stack package, several unpackaged bare chips or packaged chips are vertically stacked. In this technology, it is very important to properly interconnect the stacked chips both electrically and physically. A soldering interconnection, in particular, a reflow soldering interconnection, is most widely used for the vertical interconnection of the stacked chips.
The reflow soldering technique uses a soluble metal. Devices to be joined are fixed, and then the joining areas are heated so that the metal is melted and the solder is joined. The composition used in the reflow soldering may be a tin-lead (Sn--Pb) alloy or a tin-lead-silver (Sn--Pb--Ag) alloy in which a minute amount of silver is added. The reflow soldering technique is classified as either a vapor phase reflow soldering, an infrared reflow soldering, or a hot air reflow soldering, based upon the type of heat transfer mechanism used in the joining areas.
A conventional reflow soldering apparatus, for example as disclosed in U.S. Pat. No. 5,236,117, is shown in FIGS. 1A and 1B. A stacked package 12 to be soldered is plated with a flux and then fixed to the left end 10a of an impact arm 10. Metal outer leads 13 on the lower side of the package are heated to a certain temperature and dipped into a molten solder fountain 8. The impact arm 10 is pivotally mounted on pivot assembly 6, which allows the left end 10a of the impact arm holding the package device to move upward and downward. The impact arm 10 is shown in an elevated position in dashed lines and in the lowered position in solid lines in FIG. 1A. When the impact arm 10 moves to its lower position, the outer leads 13 of the package are dipped into the molten solder 11 in the fountain 8. A height stopper 2 is used to set the lowered position of the impact arm. Vibration means 4 vibrates the impact arm 10 in order to prevent solder voids or lack of solder tinning of closely-spaced leads.
With this dipping technique, the solder application can be performed efficiently. However, as the lead pitch gets finer as the package device requires more and more I/O pins, solder bridges may occur thereby causing electrical shorts between the leads. To alleviate these problems, impact weight 9 drops onto the top of the opposite end of the impact arm 10. Therefore, the package device 12 and the impact arm 10 are rapidly returned to the upper position, so that any excess molten solder is removed from the leads. The movement of the impact weight 9 is controlled by an air cylinder 7 which in turn may be controlled by a programmable controller.
In the conventional soldering apparatus the vertically stacked individual packages are loaded onto the apparatus manually. Furthermore, vertical interconnection into three dimensional stack package devices is suitable for J-leaded type individual packages such as SOJ (Small Outline J-bend), TSOJ (Thin SOJ) and PLCC (Plastic Leaded Chip Carrier). Thus, if an automated stacking and soldering apparatus is provided exclusively for production of J-lead type package, mass production of stack package devices is possible.